CN111355312A

CN111355312A - High speed induction machine

Info

Publication number: CN111355312A
Application number: CN201911329063.0A
Authority: CN
Inventors: H.C.卡马克; E.K-C.陈; J.A.克克; P.盖德斯-平托
Original assignee: Teco Westinghouse Motor Co
Current assignee: Teco Westinghouse Motor Co
Priority date: 2018-12-20
Filing date: 2019-12-20
Publication date: 2020-06-30
Anticipated expiration: 2039-12-20
Also published as: CN111355312B; US11258322B2; DE102019008251A1; US20200204022A1

Abstract

In one embodiment, a high speed induction machine comprises: a stator formed of a first plurality of laminations having a thickness of less than about 0.01 inches and a winding including a coil formed of litz wire adapted around the stator; and a rotor fitted within the stator. The rotor may include: a rotor core formed from a second plurality of laminations having a second thickness greater than about 0.10 inches and formed from high strength steel and sandwiched between a first end region including at least one first peripheral second lamination and a second end region including at least one second peripheral second lamination, the first end region having a first endring retained by a first retaining ring adapted thereabout and the second end region having a second endring retained by a second retaining ring adapted thereabout.

Description

High speed induction machine

The present invention was made with government support under grant number DE-EE0007254 granted by the U.S. department of energy. The government has certain rights in the invention.

Background

An induction machine includes a stator and a rotor. The induction machine operates as follows: wherein the current in the rotor is obtained by electromagnetic induction via the magnetic field of the stator windings. Induction machines are used in many different types of applications, including many industrial applications. While conventional induction machines may suitably operate at low operating speeds typical for many facilities (e.g., at a frequency of 60 hertz (Hz)), there are a number of technical challenges, including mechanical and electromagnetic stresses and losses, that can exist when the machine is to operate at high speeds. These challenges increase as the desired operating speed increases. To date, current efforts have not addressed all of the problems.

Disclosure of Invention

In one aspect, a high speed induction machine includes: a stator formed from a first plurality of laminations, each of the first plurality of laminations having a thickness of less than about 0.01 inches, wherein the stator has a winding comprising a coil formed from litz wire adapted around the stator; and a rotor fitted within the stator. In an embodiment, the rotor comprises: a rotor core formed from a second plurality of laminations, each of the second plurality of laminations having a second thickness greater than about 0.10 inches, the second plurality of laminations being formed from high strength steel and sandwiched between a first end region including at least one first peripheral second lamination and a second end region including at least one second peripheral second lamination, the first and second peripheral second laminations having a third thickness, the third thickness being greater than the second thickness, the first end region having a first endring retained by a first retaining ring adapted therearound, the second end region having a second endring retained by a second retaining ring adapted therearound.

In an embodiment, the stator may comprise a single radial ventilation duct adapted at a substantially axial midpoint of the stator. Furthermore, the high speed induction machine may be cooled via reverse ventilation to be received via a single radial ventilation duct. The reverse ventilation may circulate from a substantially axial midpoint of the stator to a first circumferential axial portion of the stator and a second circumferential axial portion of the stator.

In another embodiment, the stator may have a substantially cylindrical ductless configuration. Also, the high speed induction machine may be cooled via a cooling airflow to be received at a first circumferential axial portion of the stator and exhausted from the stator at a second circumferential axial portion of the stator.

In an example, the stator comprises a plurality of axial slots, each axial slot formed by a pair of the plurality of inner radial stator teeth, wherein each of the plurality of axial slots is to receive a first coil portion of a winding and a second coil portion of a winding and provide at least one axial passage for a cooling air flow. The at least one axial passage may be substantially adjacent to an air gap between the stator and the rotor. The first coil portion may be separated from the second coil portion via a non-magnetic spacer, providing a first axial passage for a cooling air flow.

In an embodiment, the rotor core comprises a substantially cylindrical ductless configuration. The surface of the rotor core may be formed with a grooved surface to reduce losses. The grooved surface may include a plurality of individual circumferential grooves that are fitted around the circumference of the rotor core.

In an embodiment, the rotor core further comprises a plurality of rotor bars adapted within a corresponding plurality of slots of the rotor core, wherein each of the plurality of slots comprises a slot opening to a radially outer portion of the rotor core having a width that is substantially narrower than a width of the corresponding rotor bar to provide stress relief to prevent hoop stress and minimize leakage flux (leakageflux).

In another aspect, a high speed induction machine includes a frame, a stator, and a rotor. The frame may have a first passage to receive a flow of cooling air, a second passage to receive a flow of first exhaust air, and a third passage to receive a flow of second exhaust air. The stator may be fitted within the frame and formed of a first axial portion having a first plurality of laminations and a second axial portion having a second plurality of laminations, each of the first and second pluralities of laminations having a thickness of less than about 0.01 inches. In the axial direction, the stator comprises a single radial ventilation duct adapted between the first and second axial portions, the single radial ventilation duct having a plurality of fins to direct the cooling air flow received via the first channel radially inwards. The cooling airflow may be directed through the first axial portion and output through the second passage and through the second axial portion as a first exhaust airflow and through the third passage as a second exhaust airflow. The stator may further include a plurality of inner radial teeth and a plurality of inner axial slots formed between pairs of the plurality of inner radial teeth, wherein each of the plurality of inner axial slots is to receive a first coil portion and a second coil portion of one or more coils adapted around the stator and provide a first air passage adapted between the first coil portion and the second coil portion and a second air passage adapted between the second coil portion and an inner diameter of the corresponding inner radial tooth, wherein a cooling air flow is to flow through the first air passage and the second air passage. The rotor is adapted within the stator and includes a rotor core formed from a third plurality of laminations, each of the third plurality of laminations having a second thickness greater than about 0.10 inches, the third plurality of laminations being formed from high strength steel and sandwiched between first and second end regions and including at least one first peripheral lamination and at least one second peripheral lamination, the first and second peripheral laminations having a third thickness, the third thickness being greater than the second thickness, the first end region having a first endring retained by a first retaining ring adapted thereabout, the second end region having a second endring retained by a second retaining ring adapted thereabout.

In an embodiment, a single radial ventilation duct is fitted at the substantially axial midpoint of the stator. Also, high speed induction machines may be cooled via reverse ventilation, which circulates axially outward from a substantial axial midpoint of the stator.

In another aspect, a method comprises: forming a stack including a rotor core for a high speed induction machine within a manufacturing fixture, the stack comprising: a first retaining ring; a first resistance (resistance) ring to be axially and radially constrained by the first retaining ring; a first perimeter plate having a first thickness; a plurality of inner plates having a second thickness less than the first thickness, the second thickness being at least about 0.10 inches; a second perimeter plate having a first thickness; a second resistance ring; and a second retaining ring to axially and radially constrain the second resistance ring; inserting a plurality of stacking studs through the manufacturing fixture and outside the stack and locking the plurality of stacking studs to the manufacturing fixture; heating the stack to at least a first temperature to cause the stack to form a laminated rotor core; cooling the rotating shaft to at least a second temperature, the second temperature being substantially lower than the first temperature; and mounting the rotating shaft to the laminated rotor core such that there is an interference fit therebetween.

In an embodiment, the method further comprises: at least one circumferential groove is formed on an outer periphery of the laminated rotor core. The method may further comprise: after heating the stack to at least a first temperature, fitting a first sleeve around an inner periphery of the laminated rotor core; mounting a rotating shaft to a laminated rotor core with a first sleeve fitted therebetween; and finishing the features of the rotating shaft with respect to the final position of the laminated rotor core relative to the rotating shaft.

In another embodiment, the method may further comprise: fitting a second sleeve around the inner periphery of the first sleeve; and mounting the rotating shaft to the laminated rotor core with the first sleeve and the second sleeve fitted therebetween.

In yet another embodiment, the method may further comprise: machining a plurality of interconnected longitudinal grooves in the rotating shaft to serve as high pressure hydraulic fluid conduits; mounting a rotating shaft to a laminated rotor core with a first sleeve fitted therebetween; and applying a high-pressure hydraulic fluid between the rotating shaft and the first sleeve to expand the first sleeve and the laminated rotor core while applying a force to position the laminated rotor core on the rotating shaft. The method may further comprise: processing a tapered thread around an inner hole of the laminated rotor core; machining a tapered thread on a circumferential surface of the rotating shaft; applying a torque to the rotating shaft to a selected interference level; and finishing the features of the rotating shaft with respect to the final position of the laminated rotor core relative to the rotating shaft.

Drawings

Fig. 1 is an illustration of a stator according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of a stator according to an embodiment.

Fig. 3 is an illustration of a rotor according to an embodiment.

FIG. 4 is a cross-sectional view of a rotor according to an embodiment.

FIG. 5 is an illustration of a manufacturing environment according to an embodiment.

FIG. 6 is an illustration of a rotor and shaft installation according to an embodiment.

Fig. 7A-7B are illustrations of a method of mounting a shaft to a rotor according to another embodiment.

FIG. 8 is an illustration of a rotor and shaft installation according to another embodiment.

FIG. 9 is an illustration of a rotor and shaft installation according to yet another embodiment.

Fig. 10A is a cross-sectional view of a high speed induction machine environment according to an embodiment.

Fig. 10B is a side cross-sectional view of the environment of fig. 10A, according to an embodiment.

FIG. 11A is a cross-sectional view of a high speed induction machine environment according to another embodiment.

FIG. 11B is a side cross-sectional view of the environment of FIG. 11A, according to an embodiment.

Detailed Description

In various embodiments, a high speed induction machine is provided having a plurality of rotor and stator features that enable high speed operation while ensuring mechanical stability, reducing electrical losses, and the like. In addition, embodiments provide mounting techniques to form the rotor and mount the rotor core to the rotating shaft that ensure mechanical integrity while making manufacturing simple and avoiding the need to use stacked studs as in conventional manufacturing that may negatively impact mechanical stability due to the need to form through holes along the axial length of the rotor core.

It should be understood that high speed induction machines as described herein may be used in many different applications, including motor drive (motoring) and generator applications. As used herein, the term "high speed" with respect to an induction machine is used to refer to a machine having a peripheral speed of at least 150 meters per second. Where the rotor is sized to be about 10 inches, the peripheral speed translates to a speed of at least 11270 RPM in revolutions per minute.

High speed induction machines as described herein may be included in a given system with a drive system or other power converter that may operate at megawatts levels. Furthermore, due to the high-speed nature of the machine, in embodiments, the power converter (which may be implemented as a modular power converter) may include high-speed switching devices, e.g., based on silicon carbide (SiC) technology. The combination of megawatt-based modular power converters and high-speed induction machines herein can be used in many different applications and can be used for incorporation into a system coupled between a utility grid and one or more electrical or mechanical loads and/or sources.

Referring now to fig. 1, a diagram of a stator is shown, according to an embodiment of the present invention. As shown in fig. 1, the stator 100 is formed from a stator stack 110, which itself is formed from a plurality of laminations. In embodiments herein, the laminations may be ultra-thin stator core laminations to reduce losses. In particular embodiments, the ultra-thin laminations can have a thickness of between about 0.005 inches and 0.010 inches, and in particular embodiments, the ultra-thin laminations can have a thickness of about 0.010 inches. In contrast, low speed induction machines have typical stator laminations that are about 0.02 inches thick. Although the embodiments may vary, in one embodiment, the ultra-thin laminations may be formed from cold rolled fully processed non-oriented electrical steel having very low electrical losses (about 12W/kg at 400 Hz, 1.0 Tesla, and only 1W/kg at 60 Hz). For high speed applications, to minimize core losses on the stator laminations, the stack 110 may be configured with laminations to minimize eddy currents in the laminations.

As further shown in fig. 1, a single radial ventilation duct 120 is disposed substantially at the axial midpoint of the stator 100, sandwiched between two separate lamination stacks of the stator stack 110. In an embodiment, the ventilation duct 120 may have a width of between about 1.75 inches and 2.25 inches, and in particular embodiments may have a width of about 2.0 inches. Such pipes may be wider than conventional core pipes. With a single ventilation duct as in the embodiment of fig. 1, an equal air distribution over both ends of the stator 100 can be ensured, minimizing recirculation. Although an arrangement with a single radial ventilation duct as in fig. 1 may be used in many embodiments, in other embodiments it is possible for a high speed induction machine to have a stator formed into a substantially cylindrical shape and having a ductless configuration. Rather, as further described herein, given an internal air gap or channels formed in various ways as further described herein, cooling may be achieved inside the stator core. Note that these air gaps and passages may exist in both ductless stator configurations and stator configurations with a single radial ventilation duct.

The stator stack 110 is fitted to the corresponding end plate 140₁、140₂In the meantime. In the illustration of fig. 1, it is noted that at a first end of the stator 100, to which the end plate 140 is fitted, a plurality of fingers 130 are provided. If the magnetic material is too close to the winding end turns (winding end turn), the fringing fields from the coil can generate eddy currents in the material and additional losses inside the machine, so the fingers 130 and end plates 140 are made of non-magnetic material with very low conductivityTo minimize leakage flux eddy current losses. In an embodiment, these components may be formed from a stainless steel alloy.

Referring now to fig. 2, a cross-sectional view of a stator is shown, according to an embodiment. In the cross-section of fig. 2, a single stator lamination 200 is shown. As seen, the stator lamination 200 includes a plurality of axial air slots 215 formed as recesses in the stator lamination 200 that provide a housing for the coils and air gap to enable additional cooling air flow. More specifically, stator lamination 200 includes a plurality of radially inwardly extending radial teeth, representative of which are shown as

radial teeth

202, 204, with representative axial air slots 215 formed between the

radial teeth

202, 204.

In inset 210, note that there is a coil 212 circumscribed by a wedge 219, which is made of a non-magnetic material. Below the wedge 219 there is a recessed air passage 215 through which cooling air can flow. The radial teeth of stator laminations 200 extend to the inner diameter at point 218. Note that in the inset 210, only a single coil portion is shown. However, as more fully illustrated in inset 220, each axial air slot 215 may receive two coil portions, namely

coil portions

224 and 222. In an embodiment, the coils of the stator windings may use litz wire (Litzwire) made of compacted film insulated magnet wire that is transposed (transposed) along the length to minimize excessive ac losses due to high frequency operation due to the proximity of the wires in the wire bundle. These losses can be up to 20 times higher without transposition of the litz wires at a frequency of 500 Hz.

As illustrated in inset 220, the axial air slots 215 provide additional axial air conduits to facilitate stator coil cooling. The spacer 225, as fitted between the

coil portions

222, 224, operates as an air duct spacer, providing additional air passages for the cooling air flow. It is further noted that the

coil portions

222, 224 are recessed with axial air slots 215 so that there is an open geometry and it can be used to accommodate additional cooling air flow. Thus, in either the ducted or ductless configuration of the stator, sufficient air passages are provided within the stator 200 to accommodate the cooling air flow. Although shown in this particular embodiment in fig. 2, other configurations of the stator laminations are possible.

Referring now to fig. 3, a diagram of a rotor is shown, according to an embodiment. As shown in fig. 3, the rotor 300 may be formed from a rotor core 310 itself, which is formed from a plurality of laminations (e.g., in the form of plates). The rotor core 310 is a non-solid core, i.e. has an open cylindrical shape with an opening 305 that is substantially dimensioned for receiving a rotating shaft. As will be described herein, the rotor core 310 may be sized with respect to a corresponding rotational axis to have a heavy interference fit. Axially, the rotor core 310 is fitted in the first resistance ring 320₁And a second resistance ring 320₂In the meantime. In turn, the resistance ring 320 itself with a corresponding retaining ring 330₁、330₂Is a boundary. Note that the resistance ring 320 may function as a shorting ring to which a plurality of rotor bars (e.g., formed of copper or a high strength copper alloy) are connected.

In various embodiments, the rotor core 310 may be formed of a high strength material, such as implemented with a number of laminations or plates. This is so because high rotor speeds create high hoop stresses on the rotor components. Therefore, high strength high permeability materials (e.g., heat treated 4340 steel) are used to withstand mechanical stresses. As used herein, the term "high strength" with respect to a material refers to a given material having a strength of approximately at least 100 kilogram pounds per square inch (ksi), as opposed to a low strength material, such as silicon or carbon steel, having a strength of less than about 50 ksi.

Thick laminations are used for the rotor core 310 to prevent buckling due to high interference between the laminations and the rotor shaft. In an embodiment, the lamination thickness can be between about 0.125 "and 0.250". Extremely thick laminations (e.g., having a thickness between 0.375 "and 0.500") may be installed at each end of the rotor core 310 to reduce the risk of buckling. Also, in particular embodiments, the inner rotor laminations may be formed from high strength steel plates having a thickness greater than about 0.175 inches, and the end rotor laminations (e.g., a single peripheral plate on either axial end) may have a thickness of about 0.50 inches.

In the illustration 340 showing a cross section of a single rotor core plate, note that there are no ventilation ducts, although there are a plurality of slots 345 through which the rotor bars are inserted. In contrast, conventional radial rotor tubes are produced using steel plates or I-beams sandwiched between stacks of laminations. Conventional axial ducts or openings in the rotor laminations allow air to pass axially through the rotor. However, conventional axial openings may generate significant stresses under high speed conditions. During high speed operation, steel plates or I-beams may fly out and cause catastrophic damage.

In contrast, for embodiments, there are only minimal openings 355 extending from the corresponding slots 345, as illustrated in inset 350. Openings 355 provide stress relief to prevent hoop stress and also minimize leakage flux-induced eddy current losses and improve power factor. The opening 355 may have an extremely small width, for example, approximately about 0.015 inches. In any case, the thickness of rotor bar slot opening 355 may be substantially narrower than the thickness of the corresponding rotor bar 360. As an example, the rotor bars 360 may be formed with a generally trapezoidal cross-section and may have a width of between about 0.2 inches and 0.4 inches on a radially outward end and a depth of between about 1 inch and 2 inches on a radially inward end.

In an embodiment, the rotor core 310 may be formed with a grooved rotor surface to reduce stray losses. For high speed/high frequency applications, high surface and pulsating losses may produce extreme heating on the rotor surface. The grooved rotor surface helps to break up (break up) eddy currents and minimize losses. In various embodiments, the grooved outer surface of the rotor core 310 may be formed with a plurality of substantially circumferential grooves. In another embodiment, a single helically adapted circumferential groove may be used. The grooved surface may have a depth of about 2 millimeters and a width of about 0.5 millimeters; of course, in other embodiments, other dimensions are possible.

In an embodiment, the end region of the rotor core experiences high stress due to high speed centrifugal forces. Thus, the resistance ring 320 may be formed of a high strength copper alloy. In turn, the retaining ring 330 is formed from a high strength alloy steel for protecting this area. In a particular example, the retaining ring 330 may be formed from the same high strength steel used to form the lamination plates of the rotor core 310. Additionally, the retaining ring 330 is designed to balance the tendency of the resistance ring 320 to deform into a conical shape and provide a uniform support pressure that constrains the resistance ring 320 both axially and radially.

More specifically, in fig. 4, a cross-sectional view of a rotor according to an embodiment is illustrated. Here, the rotor 300 includes a resistance ring 320 constrained by a corresponding retaining ring 330. As further shown, note that the end plate of rotor 300 (i.e., end plate 310)_E) May be formed of a thicker laminate (e.g., between 0.375 inch and 0.5 inch) than the other laminates. Of course, in some embodiments, end plates having a greater thickness than the inner plates of the rotor core may be provided.

As described above, in an embodiment, the end plate 310_EAnd the retention ring 330 may be formed from the same high-strength steel material, whereas, instead, the drag ring 320 is formed from a high-strength copper alloy to which a plurality of rotor bars may be adjoined (e.g., via brazing). Also as shown by the direction of the arrows in fig. 4, at high speed operation, centrifugal force causes an outward pressure on the resistance ring 320. Where the geometry of the resistance ring 320 has a tapered profile (as shown at the point where the arrows meet) and the corresponding shape of the retaining ring 330 is fitted around that point, a proper balance of opposing forces is achieved.

Fig. 4 also shows that when fitted to each other, there may be a small axial space between the resistance ring 320 and the retaining ring 330 (at various points of the axial profile), providing room for expansion during manufacture and operation. In contrast, there is very limited or no space at the radial point where the resistance ring 320 and the retaining ring 330 contact each other (where the arrows meet). As further shown, note that the center of mass of the retaining ring 330 is disposed substantially axially away from the retaining ring's point of contact to provide a counterbalancing force.

Embodiments also provide a number of different methods of forming a rotor and adapting a shaft to the rotor. More specifically, with embodiments, a rotor as described herein may incorporate thick laminations, end plates, and lock nuts by means of a heavy interference fit to eliminate the need for stacking studs. That is, in conventional processes, conventional stacked rotors are formed using stacking studs that extend through pre-existing holes in the rotor laminations to provide the proper stacking pressure. However, these pre-existing holes and the inclusion of stacked studs adversely affect performance. This is so because these holes produce high hoop stresses even when filled with stacked studs. In contrast, with embodiments, core pressure is maintained and lamination deformation is minimized after the manufacturing fixture has been removed. More specifically, core pressure may be maintained through the use of thick laminations, heavy shrink fit, and lock nuts against the end plates. The lock nut is installed and torque applied immediately after installation of the core but before removal of the fixture. This stacking technique allows for simplification of the rotor lamination geometry and eliminates the need for any additional holes in the laminations as in conventional processes.

Referring now to FIG. 5, an illustration of a manufacturing environment is shown, according to an embodiment. As shown in fig. 5, in a manufacturing environment 500, a manufacturing fixture 510 is provided. As can be seen, the rotor stack 310 may be formed on a fixture 510. When fitted to the fixture 510, corresponding resistance rings and retaining rings are provided in the stack in addition to the lamination plates. In contrast to conventional manufacturing processes, instead of providing internally (to the rotor stack) included studs, a plurality of external stack studs 520 are fitted around the circumference of the fixture 510 and used to lock the fixture 510 into place to provide a stacking force on the stacked arrangement of the rotor cores 310 from the external position.

After this stacking process, fixture 510 may be placed in an oven or other heating mechanism to raise the temperature of rotor core 310 to enable an abutment process with the rotor shaft (not shown in fig. 5). As an example, the rotor stack 310 may be heated to a temperature between approximately 375 degrees celsius (° c) and 425 degrees celsius (° c) for a duration of at least 8 hours to cause the individual laminations to radially expand.

Thereafter, to assemble the rotor core to the rotor shaft, the rotor shaft may be cooled to an appropriate temperature. For example, the rotor shaft may be placed in dry ice for a period of between about 4 hours and 8 hours to reach a temperature approximately between about-50 ℃ and-100 ℃. After this cooling process and when the rotor core is at a high temperature (e.g., at least 375 ℃), an abutment process may occur in which the rotor shaft is mounted within the rotor core. When the hot metal of the rotor core engages the cold metal of the rotating shaft, the rotating shaft is thus heated and expands to achieve the desired level of interference fit between the rotating shaft and the rotor core.

For large rotor diameters, another alternative rotor-to-shaft assembly technique may be used. This is so because as the rotor lamination diameter increases above about, for example, 12 inches, the amount of interference fit required with the shaft increases to the point where the laminations cannot be heated sufficiently to fit on the shaft. This is because the amount of heat required for assembly will negatively impact the material properties of the laminate.

Thus, the stacked rotor laminations of the rotor core may be mounted with the shaft and a high level of interference is achieved by using concentric tapered sleeves. In this technique, the stacked rotor cores are heated to the highest allowable level (e.g., approximately 400 ℃) and shrink-fit to a sleeve, which may be formed of the same high strength steel as the rotor cores and tapered in inside diameter. The assembly is again reheated to the maximum allowable level and placed on the shaft. At this point, the inner segmented sleeve is installed and tightened with a lock nut.

Thus, as shown in fig. 6, in the resulting arrangement of the process, a rotor 600 is obtained, which includes a rotor core 610 and a rotating shaft 620. Note that there is an outer core sleeve 612 with a tapered bore and an inner segmented sleeve 614 inside with a tapered outer diameter. Additionally, fig. 6 shows the presence of a core compression nut 630 and a shrink-fit securing nut 635, both of which are adapted to constrain the arrangement about the shaft 620 and about at least a portion of the

sleeves

612, 614.

In another embodiment, the stacked core is heated to the highest allowable level and shrink-fitted to a sleeve with a tapered inner diameter. A retaining nut is mounted at one end of the tapered sleeve to maintain the stack pressure. The assembly is then reheated to the highest allowable level and placed on the tapered shaft and pressed until the desired interference is thereafter achieved. A lock may be installed to hold the stacked cores and the shaft installation completed.

Fig. 7A shows a first step of the manufacturing process, where a retaining nut 730 is mounted at one end of a tapered sleeve 712, which in turn is fitted between the rotor core 710 and a tapered shaft 720, which may be pre-machined. After the process is complete, fig. 7B shows a second step of the process, where the features of the tapered shaft 720 may be finished to provide a desired shape for the purpose of final position with respect to the rotor core 710 and for being fitted within a particular high speed machine frame to mate with bearings and the like.

In yet another embodiment as shown in fig. 8, stacked rotor core 810 is stacked between two end plates and compression is maintained using a fixture similar to that described in fig. 5. Both the outer diameter of the shaft 820 and the inner diameter of the stacked core 810 are threaded. Special fixtures and tools (tolling) may be used to apply torque to the stacked cores to achieve the desired level of interference depending on the measurement of the diameter growth of the outer diameter. After the proper interference has been achieved, the shaft is finished.

In yet further embodiments, as shown in fig. 9, the stacked core 910 can be stacked between two end plates 912, 914 and maintained in compression using a sleeve 920 having a locking nut 925 at one end. The bore of the sleeve 920 is tapered. The stacked core 910 can be mounted to an appropriate interference via a plurality of longitudinal grooves 935 in the shaft 930 using high pressure hydraulic fluid to expand the sleeve 920 as it is pressed onto the shaft 930.

Reverse ventilation of high speed induction machines may occur using a high speed motor having a stator with a single, substantially axially centrally located ventilation duct. With this arrangement, cooled air driven by an external blower enters the machine from the center and circulates back on both ends of the machine. Since the high speed rotor has no ducts or internal blowers, an external blower is used to create internal air circulation. The external blower provides consistent air flow in variable speed applications and/or adjustable air flow as needed depending on the operating conditions of the machine. In contrast, conventional machine configurations with rotors having axial and radial ventilation ducts will typically produce an internal air flow.

Referring now to FIG. 10A, a cross-sectional view of a high speed induction machine environment is shown, according to an embodiment. As shown in fig. 10A, machine environment 1000 includes a frame 1010 that houses a high-speed induction machine 1005 formed of a stator and a rotor (with corresponding assembled shafts, as described herein). In the embodiment of fig. 10A, a reverse draft cooling arrangement is shown in which cooling air is received from a (e.g., external) cooler via air flow 1020 through first channel 1025. The cooling air then flows down and into the machine 1005 via a single radial ventilation duct 1015. Cooling air flows through the air gap and air passages within the stator (as described herein) and the air gap between the stator and the rotor. After exiting from either axial end of the stator through the stator windings, the air exits as

exhaust streams

1030, 1040 via the second and

third passages

1035, 1045, respectively, back to the cooler for further cooling. FIG. 10B also shows a side view with cooling air flow.

In another embodiment, a single ventilation technique may be used, where cooled air driven by an external blower enters the machine from one end and circulates back through the air gap to the other end of the machine. Referring now to FIG. 11A, a cross-sectional view of a high speed induction machine environment is shown, according to another embodiment. As shown in fig. 11A, machine environment 1100 includes a frame 1110 that houses a high-speed induction machine 1105 formed from a stator and a rotor (with corresponding assembled shafts, as described herein).

In the arrangement of fig. 11A, in the case of a ductless stator, cooling air from the cooler enters the frame 1110 through the first channel 1125 and via an air gap between the rotor and the stator and an air channel as described herein as an air stream 1120 at a first circumferential axial portion of the machine 1105, the cooling air stream passing axially through the machine 1105 and exiting as an exhaust stream 1130 via the channel 1135 to the cooler. FIG. 11B also shows a side view with cooling flow.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Claims

1. A high speed induction machine, comprising:

a stator formed from a first plurality of laminations, each of the first plurality of laminations having a thickness of less than about 0.01 inches, wherein the stator has a winding comprising a coil adapted around the stator, the coil formed from litz wire; and

a rotor adapted within the stator, the rotor comprising:

a rotor core formed from a second plurality of laminations, each of the second plurality of laminations having a second thickness greater than about 0.10 inches, the second plurality of laminations being formed from high strength steel and sandwiched between a first end region including at least one first peripheral second lamination and a second end region including at least one second peripheral second lamination, the first and second peripheral second laminations having a third thickness, the third thickness being greater than the second thickness, the first end region having a first endring retained by a first retaining ring adapted thereabout, the second end region having a second endring retained by a second retaining ring adapted thereabout.

2. The high speed induction machine of claim 1, wherein the stator comprises a single radial vent conduit adapted at a substantially axial midpoint of the stator.

3. The high speed induction machine of claim 2, wherein the high speed induction machine is to be cooled via a reverse draft to be received via the single radial vent duct.

4. The high speed induction machine of claim 3, wherein the back draft will circulate from the substantially axial midpoint of the stator to a first circumferential axial portion of the stator and a second circumferential axial portion of the stator.

5. The high speed induction machine of claim 1, wherein the stator comprises a substantially cylindrical ductless configuration.

6. The high speed induction machine of claim 5, wherein the high speed induction machine is to be cooled via a cooling air flow to be received at a first circumferential axial portion of the stator and exhausted from the stator at a second circumferential axial portion of the stator.

7. The high speed induction machine of claim 1, wherein the stator comprises a plurality of axial slots, each axial slot formed by a pair of a plurality of inner radial stator teeth, wherein each of the plurality of axial slots is to receive a first coil portion of the winding and a second coil portion of the winding and provide at least one axial passage for a cooling air flow.

8. The high speed induction machine of claim 7, wherein the at least one axial channel is substantially adjacent an air gap between the stator and the rotor.

9. The high speed induction machine of claim 7, wherein the first coil portion is separated from the second coil portion via a non-magnetic spacer, thereby providing a first axial passage for the cooling air flow.

10. The high speed induction machine of claim 1, wherein the rotor core comprises a substantially cylindrical ductless configuration.

11. The high speed induction machine of claim 10, wherein the surface of the rotor core comprises a grooved surface to reduce losses.

12. The high-speed induction machine of claim 11, wherein the grooved surface comprises a plurality of individual circumferential grooves fitted around the circumference of the rotor core.

13. The high speed induction machine of claim 1, wherein the rotor core further comprises a plurality of rotor bars fitted within a corresponding plurality of slots of the rotor core, wherein each of the plurality of slots comprises a slot opening to a radially outer portion of the rotor core having a width that is substantially narrower than a width of the corresponding rotor bar to provide stress relief to prevent hoop stress and minimize leakage flux.

14. A high speed induction machine, comprising:

a frame having a first passage to receive a flow of cooling air, a second passage to receive a flow of first exhaust air, and a third passage to receive a flow of second exhaust air;

a stator fitted within the frame, the stator formed of a first axial portion having a plurality of first laminations and a second axial portion having a plurality of second laminations, each of the plurality of first laminations and the plurality of second laminations having a thickness of less than about 0.01 inches, wherein, in an axial direction, the stator includes a single radial vent duct fitted between the first axial portion and the second axial portion, the single radial vent duct having a plurality of fins to direct the cooling air flow received via the first channel radially inward, wherein the cooling air flow is to be directed through the first axial portion and output through the second channel and through the second axial portion as the first exhaust air flow and through the third channel as the second exhaust air flow, the stator comprising a plurality of inner radial teeth and a plurality of inner axial slots formed between pairs of the plurality of inner radial teeth, wherein each of the plurality of inner axial slots is to receive a first coil portion and a second coil portion of one or more coils adapted around the stator and provide a first air passage and a second air passage, the first air passage being adapted between the first coil portion and the second coil portion, the second air passage being adapted between the second coil portion and an inner diameter of the corresponding inner radial tooth, wherein the cooling air flow is to flow through the first air passage and the second air passage; and

a rotor adapted within the stator, the rotor including a rotor core formed of a third plurality of laminations, each of the third plurality of laminations having a second thickness greater than about 0.10 inches, the third plurality of laminations being formed of high strength steel and sandwiched between a first end region and a second end region, and including at least one first peripheral lamination and at least one second peripheral lamination having a third thickness, the third thickness being greater than the second thickness, the first end region having a first end ring retained by a first retaining ring adapted thereabout, and the second end region having a second end ring retained by a second retaining ring adapted thereabout.

15. The high speed induction machine of claim 14, wherein the single radial vent conduit is adapted at a substantially axial midpoint of the stator.

16. The high speed induction machine of claim 15, wherein the high speed induction machine is to be cooled via a reverse draft that circulates axially outward from a substantially axial midpoint of the stator.

17. A method, the method comprising:

forming a stack including a rotor core for a high speed induction machine within a manufacturing fixture, the stack comprising: a first retaining ring; a first resistance ring to be axially and radially constrained by the first retaining ring; a first perimeter plate having a first thickness; a plurality of inner plates having a second thickness less than the first thickness, the second thickness being at least about 0.10 inches; a second perimeter plate having the first thickness; a second resistance ring; and a second retaining ring to axially and radially constrain the second resistance ring;

inserting a plurality of stacking studs through the manufacturing fixture and outside the stack and locking the plurality of stacking studs to the manufacturing fixture;

heating the stack to at least a first temperature to cause the stack to form a laminated rotor core;

cooling the rotating shaft to at least a second temperature, the second temperature being substantially lower than the first temperature; and

the rotating shaft is mounted to the laminated rotor core such that there is an interference fit therebetween.

18. The method of claim 17, further comprising: at least one circumferential groove is formed on an outer periphery of the laminated rotor core.

19. The method of claim 17, further comprising:

after heating the stack to at least the first temperature, fitting a first sleeve around an inner periphery of the laminated rotor core;

mounting the rotating shaft to the laminated rotor core with the first sleeve fitted therebetween; and

finishing features of the rotating shaft with respect to a final position of the laminated rotor core relative to the rotating shaft.

20. The method of claim 19, further comprising:

fitting a second sleeve around an inner periphery of the first sleeve; and

mounting the rotating shaft to the laminated rotor core with the first sleeve and the second sleeve fitted therebetween.

21. The method of claim 19, further comprising:

machining a plurality of interconnected longitudinal grooves in said rotating shaft for use as high pressure hydraulic fluid conduits;

applying a high pressure hydraulic fluid between the rotating shaft and the first sleeve to expand the first sleeve and the laminated rotor core while applying a force to position the laminated rotor core on the rotating shaft.

22. The method of claim 17, further comprising:

machining a tapered thread around an inner hole of the laminated rotor core;

machining a tapered thread on a circumferential surface of the rotating shaft;

applying torque to the laminated rotor core to the rotating shaft to a selected interference level; and